Here are some recommendations:

Have your boiler serviced annually, this increases efficiency of your home heating, i.e the more efficient the boiler, the more heat is extracted from the oil burned.

Consider replacing your older boiler with a more energy efficient condensing boiler.

Turn the thermostat on your boiler down as low as
is comfortable.

Turn heaters down or off in all the rooms you rarely use and also get into the habit of adjusting your radiators as the
seasons change.

When was the last time you ‘bled’ your radiators. It is inevitable that you will get some air into your heating system and it tends to accumulate at the top of your radiators, usually in rooms upstairs. This air slows your radiator heating up and in extreme circumstances can prevent a radiator heating at all.